Procedure for controlling a multistand rolling mill

ABSTRACT

A METHOD OF CONTROLLING THE TRACKING OF A TRAVELING STRIP OF MATERIAL BEING REDUCED IN THICKNESS BY THE WORKING ROLLS OF A MULTISTAND MILL. THE METHOD INCLUDES THE STEPS OF MEASURING THE ROLLING FORCE ADJACENT THE ENDS OF THE WORKING ROLLS TO PROVIDE FORCE-DIFFERENTIAL INFORMATION FOR EACH STAND OF THE MILL. THIS INFORMATION IS MONITORED WITH REFERENCE TO A TIME BASE, AND WHEN FORCE-DIFFERENTIALS OCCUR INDICATING AN ERROR IN STAND LEVEL OR FRICTIONAL FORCES, CORRECTION OF STAND LEVEL AND/OR FRICTIONAL FORCES ARE EFFECTED IN A PREDETERMINED PROCEDURE ON THE BASIS OF THE TIME BASED, FORCE-DIFFERENTIAL INFORMATION.

Oct. 19; 1971 w, A.WQODBURN I 3,613,417

PROCEDURE FOR CONTROLLING A MULTISTAND ROLLING MILL Filed Feb. 1970 2 Shets-Sheet 1 FIG. 5.

T U o L I M lNl/EN TOR. WILTON A. WOOOBURN NOSE IN Allarney W. A. WOODBURN Oct. 19', 1971 PROCEDURE FOR CONTROLLING A MULTISTAND ROLLING MILL 2 Sheets-Shoat 2 Fla. 4

Filed Feb. 9, 1970 FIG. 3.

- 4/ IIIIIIIII/ FROM RE MA I IV/NG STANDS N l/EN ran. wn. row A. woooaumv Attorney United States Patent Oliice 3,613,417 PROCEDURE FOR CONTROLLING A MULTISTAND ROLLING MILL Wilton A. Woodburn, Lower Burrell, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa. Filed Feb. 9, 1970, Ser. No. 2867 Int. Cl. B21b 37/00 U.S. Cl. 72-8 3 Claims ABSTRACT OF THE DISCLOSURE A method of controlling the tracking of a traveling strip of material being reduced in thickness by the working rolls of a multistand mill. The method includes the steps of measuring the rolling force adjacent the ends of the working rolls to provide force-differential information for each stand of the mill. This information is monitored with reference to a time base, and when force-differentials occur indicating an error in stand level or frictional forces, correction of stand level and/or frictional forces are effected in a predetermined procedure on the basis of the time based, force-differential information.

BACKGROUND OF THE INVENTION The present invention relates generally to multistand rolling mills, and particularly to a tracking control method or procedure for quickly determining and correcting certain undesired or error conditions in the mill.

Expanding markets for rolled metallic sheet have demanded greater quantities and better quality at lower cost. An important element in meeting these demands has been the multistand rolling mill for both hot and cold rolling of metallic products. Such mills permit greater flexibility of control to satisfy quality requirements without intermediate handling operations, hence, lower cost. However, the potential flexibility of multistand mills has also required complex control systems to coordinate speeds and gages of the individual stands. The continuity of the system is most commonly achieved by monitoring the tension developed within the metal strip as it passes from stand to stand and regulating stand conditions to maintain some tension level. The presence of tensions effects the behavior of the material being rolled in a manner as to be self-compensating for small errors or disturbances in the system.

Most conventional systems process quantities of metal strip of finite length. Consequently, as the beginning end or nose of the strip enters successive stands there are periods where there is no tension on the leading portion, and similarly, when the final end or tail leaves successive stands there are periods when there is no tension on the trailing portion. During these unique periods there is little or no self-compensation and the mill may be sensitive to small errors. In particular, this may be accompanied by a movement of the nose or tail away from the centerline of the mill. The condition of causing all portions of the strip to follow the centerline of a multistand mill is called tracking. Tracking in the present invention, as explained in detail hereinafter, is related to the lateral movement of strip material when the material is nonuni formly reduced in thickness in a stand or stands due to an error in stand level or friction. Failure to control tracking results in a variety of operating problems depending on 3,613,417 Patented Oct. 19, 1971 the severity of resulting error. Movement beyond the rolling face of the working rolls can tear the metal by either striking the housing containing the rolls or by pinching off material extending beyond the working faces.

Metal strip is frequently trimmed before being coiled at the end of the mill. Trimming is accomplished by rotating knives or shears located at specific distances from the mill centerline. If the nose or tail of the strip moves enough off centerline to miss the trimmer, a raw, untrimmed edge remains which must be scrapped at some later operation. Depending on the reliability with which tracking can be controlled, the amount of side trim need only be that amount that contains side cracks, original cast surface, or similar edge defects. Any greater amount to accommodate a lack of tracking control is an unnecessary loss.

Finally, whenever material moves off the mill centerline it loses its symmetry of thickness profile and such material causes a problem in most subsequent operations, for example, cold rolling operations performed on the strip produced by a hot roll mill.

When material fails to track properly it has the appearance of moving or sliding to the side particularly at high speeds. It has been an accepted tenet of the rolling art that a thickness profile of the strip, such that the center is thicker than the edges combined with similarly configured and mating surfaces of the roll gap, confines the strip and restricts lateral movement. Neither of these observations are totally correct for a rolling mill wherein a substantial reduction of thickness, from 10 to percent, is achieved. The tractive conditions necessary for the roll surface to pull the metal into the roll bite and cause the required deformation are many times greater than those needed to prevent lateral slipping.

The lateral movement of the strip in tracking is a result of a nonuniform reduction across the width of the strip. Adjacent the nose of the strip, the result is a curved strip where the edge receiving an excess of reduction forms the outside of the curved section. There is no lateral movement at the rolls where the reduction is made but the effect is to move the nose off the centerline of the mill before it reaches the next stand.

The tail, however, moves by a different mechanism. The edge where less reduction has taken place is pulled into the bite of the working rolls at a greater rate than the opposite side thereby rotating the free length of the tail entering the stand needing adjustment. As the strip advances, portions of the tail that have been rotated off centerline enter the roll gap in laterally displaced locations, giving the appearance of sliding across the face of the rolls in question. As with the nose, the edge where excess reduction is taken is on the outside of the curve.

The relative reduction taken on the edges of the strip depends on the thickness profile of the strip entering a stand and the relative spacing of the roll faces forming the gap through which the strip is passed. This relative position of roll faces is called the level of the rolls or of the roll stand and is commonly adjusted by screws in the housings at each end of the rolls. Rolls can be leveled by various techniques without metal in the mill. However, the effective level of the stand may be altered during operation by the condition of the strip, by unequal thermal expansion from side to side, or by unequal distribution of separating force across the mill. The latter source of change is not as obvious but frequently the most important. The housing containing the rolls is an elastic structure such that as the separating force increases the housing stretches and the gap between working faces of the rolls increases. The relationship of stretch to load is called the mill modulus. If the effective center of the total separating force is not centered in the mill, the housing at one end of the roll is loaded heavier than the housing at the other end and the level of the stand is changed. This can be described mathematically by:

Dynamic effect on stand level:

4 (mill modulus) (total separating force) (eccentricity of force center) +(distance between screws) It is obvious from the above that in comparing different stands an increase in any of the first three factors or decrease in the last term will increase this dynamic effect on level. The force center moves away from the centerline if the strip moves off center or if the distribution of load across the roll face changes. The most important effects that cause redistribution of load are changes in friction across the roll face or changes in strip tension from one edge to the other. Differences in amount of reduction itself have a drastic effect on tracking before they become a factor in redistribution of load.

In hot rolling aluminum, for example, the frictional conditions are closely associated with the coating of aluminous material on the ferrous surface of the rolls, and this is commonly controlled by continuously scratchbrushing the roll surfaces. During running conditions, tensions are redistributed in the strip so that the dynamic level of the mill compensates for errors in mechanical level or friction distribution. During threading of the mill, tension on the entry side of a stand will partially cornpensate for such errors. However, during tail-out, any error in stand level will alter the tension distribution on the exit side of the stand in a direction that worsens the effect level of the stand by adding dynamic level to the existing errors. The stand in question not only may cause lateral movement of the tail but alters the strip profile in a manner that may become a greater problem in the next stand in succession.

It is common practice by an operator, Without other guidance, to observe movement of the nose and tail and make a correction in the mill when such movement reaches significant proportions. Visibility, however, is often obscured by a flood of coolant or envelope of vapor. Although an operators ability to separate mechanical level from frictional effects and to determine what stand requires adjustment improves with experience, it is not possible by such means to completely isolate errors nor to anticipate potential problems.

Further, as the strip travels through the mill, the speed of the strip increases because its thickness is being reduced by the successive stands. As the speed increases, it becomes increaingly more difficult for the operator to visibly observe the strip, interpret his observations and then make the necessary corrections in time without accumulating or compounding the errors in the mill. At the downstream stands he has only a fraction of a second to observe and interpret the condition causing movement of the strip.

A further disadvantage with visual control by an operator is that he tends to overcorrect for only minor errors in mill conditions, and in judging which stand to correct, he often chooses a downstream stand rather than the one causing the difficulty. In this manner, a sequence of adjust ments can easily obsecure the true cause of a tracking problem. This complicates the problem requiring extensive readjustment where only a minor adjustment may have been originally necessary.

BRIEF SUMMARY OF THE INVENTION Broadly, the present invention provides a tracking control procedure by which error conditions in a multistand mill are quickly ascertained and corrected before such errors are compounded in the mill resulting in wasted strip material and possible costly shut-down of the mill. Quick control and correction are accomplished by measuring the roll separating force or load adjacent the ends of the working rolls of each stand, and monitoring the force-differential between the roll ends with respect to a time reference to provide time based, force-differential information for each stand. This information is then used to correct stand level, frictional forces and/or reversing mill operations in the manner explained hereinafter.

THE DRAWINGS The invention, with its advantages and objectives, will become more apparent from reading the following detailed description in connection with the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of a multistand mill and stand monitoring means with which the method of the present invention is effective to control tracking of a strip being reduced by the mill;

FIG. 2 is a diagrammatic showing of a force-differential monitoring means providing forcediiferential information for one stand of the multistand mill of FIG. 1;

FIG. 3 is a plan view showing lateral movement (in increments of longitudinal travel) of the nose of a strip of material being reduced in thickness by the mill of FIG. 1;

FIG. 4 is a plan view showing lateral movement (in increments of longitudinal travel) of the tail of the strip of FIG. 4; and

FIG. 5 is a chart section of a recorder employed to simultaneously plot the force-differential information for each stand of the mill of FIG. 1 for the purposes of the present invention.

PREFERRED EMBODIMENT Specifically, FIG. 1 shows diagrammatically a five stand rolling mill ll) of the type employed to reduce the thickness of a str1p of material 12 having finite length indicated by a leading or nose portion 12A and a tail portion 12B. After traveling through the mill, the strip indicated in phantom by 12, is collected on a coiling device 14. The stands of the mill are designated respectively by numerals 1 to 5, stands 1 and 5 being respectively the first and last stands in the mill 10. Each stand of the mill is shown as a four high stand, i.e., a stand with two outer pressure rolls 18 and 19 and two inner working rolls 29 and 21 though the method of the invention is not limited to employment with only four high stands.

As indicated in FIG. 2, the front and rear sides of each stand of the mill 10 are respectively provided with leveling mechanisms 24 and 25, the mechanisms being represented by vertically disposed screws located above the necks of the upper pressure rolls 18. Between each of the screws 24 and 25 and their corresponding roll necks are located, respectively, load cells 26 and 27 for sensing the forces separating the Working rolls when they are reducing the thickness of the strip 12. The load cells may be of the inductive transducer type forming an integral part of a load sensing system, for example, as manufactured by the ASEA Company of Sweden though other load sensing devices and systems can be used for the purposes of the invention. In the view of FIG. 1, only the front screws 24 and load cells 26 are visible for each of the stands 1 through 5.

The load cells 26 and 27 for each of the stands are shown respectively electrically connected to a circuit 30 capable of measuring the difference in roll separating force between the ends of the working rolls 2t) and 21 for each stand as measured by the load cells. The circuit 34 may be an integral part of the ASEA system mentioned in which a signal conditioning device is employed to make an algebraic summation of the loads measured by the cells 26 and 27.

The output of each of the force-differential measuring circuits 30 are shown electrically connected to a chart recorder 32 to provide separate, continuous, force-differential information and indications for each stand of the mill 10. The recorder may be any of the commercially available types of recording devices providing a linear trace for each signal directed thereto on a chart 33. Preferably, the recorder has an accurately controlled chart speed to provide the information with a time base or reference though other timing means may be employed to provide such a reference. In FIG. 5, the chart of the recorder is shown having transverse time lines 34 which indicate the position of the strip 12 in the mill as explained in more detail hereinafter.

In FIG. 1, upper and lower scratch brushes 38 and 39 are diagrammatically shown respectively engaging the rolling surfaces of the upper and lower working rolls and 21. In hot rolling mills, the working rolls tend to pick up metal and other substances from the surface of the strip being rolled. This metal, if left on the rolls would directly affect the frictional forces by increasing such forces between the rolls and the strip. The scratch brushes perform a cleaning function by removing the metal from the rolls, and thereby control the amount of friction between roll and strip. The brushes extend along the length of the working rolls, and the distribution of the force with which the brushes contact the rolls can be adjusted by suitable means (not shown) for moving the brushes relative to the rolls.

In threading a multistand mill, the strip (strip 12, for example) starts through the mill by its nose portion 12A entering the bite of the working rolls of the first stand. In FIG. 1, the strip 12 enters stand 1 and passes on to successive stands 2 to 5.

During threading, if the strip is centered as it enters the rolls of a stand there will be no significant change in the force-differential for that stand regardless of the thickness profile of the strip or the level of the stand. However, if there was a level error, the nose 12A exiting from the stand will curve away from the centerline of the mill with the edge receiving the greater reduction forming the outer edge of the curve. When the nose bites into the next successive stand it will be off-center. The side and screw toward which the strip has moved will be loaded heavier than the screw at the other end of the rolls, and this will be indicated by a deflection of a corresponding trace line on chart 33 in a manner described in detail hereinafter.

FIG. 3 shows the phenomenon of the curvature and movement of the nose 12A from the mill centerline when the level of a given stand (stand 2) reduces the left edge of the strip a greater amount than the right edge as evidence by the strip cross section at 41. The phenomenon is shown in FIG. 3 by showing increments of nose travel from stand 2 to stand 3. As seen, when the leading edge of the nose 12A enters stand 3, the nose is shifted to the right and the leading corner enters the left side of the Working rolls of the stand ahead of the right side. When the nose has fully entered the roll bite, the shlft of the nose from the mill centerline causes an unequal roll separating force across the stand. This unequal force is measured by its loads cells and summed by the force-d1tferential measuring circuit 30- which provides a difference signal for the recorder 32 in a manner presently to be explained.

Thus, as mentioned earlier, an error in a g1ven stand affecting the nose of a strip is reflected in the next stand or stands. If correction is to be made, i.e., if the error is of sufficient magnitude to require correction, the given stand could be corrected while watching the behavior of the next successive stand, since the successive stand reflects the error, not the stand actually in error. An alternative procedure would be to make no change until tailout conditions have been evaluated.

As a strip travels through a mill, its tail portion leaves or drops out of each stand in the successive order of the stands. With an error in stand level on tail out, (i.e., drop out), however, the stand in error is the one to observe and thus to correct. When the tail of a strip leaves the manipulator (not shown) used to center the strip before it enters the first stand of the mill, the tail of the strip is free to move about. Similarly, as the tail leaves a stand, the tension on the strip is removed so that the tail is again free to move.

When an error in stand level occurs such that the rolls thereof reduce the thickness of a strip in a nonuniform manner across its width, the tail of the strip is rotated in the stand in error so that the tail moves from the centerline of the stand. This phenomenon is shown in the view of FIG. 4 which shows increments of longitudinal travel of the tail 12B from the working roll 21 of strand 1 to the working roll 21 of stand 2. In the figure, stand 2 is reducing the left side by the greater amount (as shown in cross section at 42) which tends to swing the tail to the right. As shown, the tail leaves stand 1 on centerline, but when the tension on tail, provided by the bite of the rolls of stand 1, is removed, the tail swings to right as the stand in error (stand 2) rotates the tail. As the tail travels towards stand 2, the lateral movement of the tail increases. As indicated, lateral movement of the tail may be such that the tail slides off the edge of the roll to be caught in the neck bearings of the rolls and in the frame housing of the stand.

As shown in FIG. 4, the tail 12B moves through stand 2 to the right of the centerline of the stand. When this occurs, the separating force between the working rolls 20, 21 will be unbalanced, the load cell on the right side of the stand measuring a load substantially greater than that of the left. The difference in rolling force is sensed by the circuit 30 which forwards this information to the recorder 32.

If the direction of the lateral movement of nose and tail are in the same direction, i.e., if the tail exiting from stand 2, for example, moves laterally in the same direction as the curve of the nose entering stand 3, as shown in FIGS. 3 and 4, a level correction can be made to stand 2 in the same direction as was previously suggested in connection with lateral movement of the nose.

If, however, the tail of the strip is rotated by a given stand in a direction opposite to the curve of the nose entering a successive stand or where there had been no movement of the nose, this is indicative of an error in roll friction of the stand rotating the tail. This can be corrected by adjusting the distribution of the force with which the scratch brushes engage the rolls along their length dimension. As explained above, the metal and other substances picked up by the working rolls from the strip tend to increase the friction between the strip and rolls. If an error occurs in the position of the scratch brushes, which function to control the metal pickup and thus friction in a uniform manner along the length of the rolls, the error in friction will be reflected in a difference in rolling force across the strip producing a dynamic level change which rotates the strip.

In accordance with the principles of the present invention, a mill, mill 10 for example, is controlled in a manner to immediately locate and correct for errors in stand level and frictional forces while the strip is being tracked through the mill before such errors are compounded in the mill. This is accomplished by watching trace lines 1' to 5' (corresponding to the stand 1 to 5) on the chart 33 of recorder 32 to determine when and where error occurs, the recorder monitoring force-differential information of each stand as provided by the force-differential circuits 30 respectively associated with each stand.

More particularly, when the strip 12 is started through the mill 10, the recorder 32 begins to plot, on the chart 33 as shown in FIG. 5 relatively straight parallel lines 1' to 5 representing the force-differential information respectively for stand 1 to 5 provide by their respective circuits 30 and load cells 26 and 27. In FIG. 5, the chart travels toward the bottom of the drawing so that the parallel lines trace from the bottom of the drawing to the top. In this manner, the time sequence is of the same order, i.e., from bottom to top.

The strip 12 starts through the mill by the nose 12A entering the bite of the working rolls 20, 21 of stand 1. This event is indicated on the chart by a slight rightward deflection of trace line I as indicated at 1A in FIG. 5, the rightward deflection indicating a slight differential in rolling force, as measured by the load cells 26 and 27.

From stand 1 the nose 12A of the strip enters stand 2 as indicated by a similar slight rightward movement of trace line 2 at 2A. From stand 2, the strip enters stand 3. However, at stand 3, there is a leftward movement imparted to trace 3' indicating that the nose has moved in that direction as it passes from stand 2 through stand 3 as indicated at 3A. Slight leftward movement is also indicated as the nose of the strip passes through stands 4 and 5. The force-differential change that occurs when the nose reaches each stand, as explained in greater detail hereinafter, is displaced from the corresponding change at the previous stand by a time interval determined by the distance between stands and by the speed of the strip between stands.

As the strip 12 moves through the stands, the tail portion 12B thereof drops out of each stand, and this drop out or tail-out is indicated by the deflections IE to 5B of the trace lines 1' to 5' near the top of the chart 33 as shown in FIG. 5. The progression of tail-out is similar to that of nose-in though the actual time intervals will be different if there has been a change in the operating speed of the mill.

Since force-differential information for all stands is monitored by the recorder 32 with reference to a common time base, it is possible to follow the progression of a disturbance through an entire multistand mill. The force-differential change that occurs when the nose reaches each stand is displaced by time interval determined by spacing between stands and the strip speed be tween those stands as mentioned above. A similar progression can be seen at tail-out. It is therefore possible to detect and differentiate between a simultaneous reaction of several stands or a reaction of successive stands to a disturbance transported by the strip. In a rolling mill, the strip being reduced in thickness thereby tends to function as a memory device carrying with it the reduction parameters it receives in each stand.

For example, if there is an error in a stand such that on tail-out the tail 12B of the strip 12 is rotated by a substantial amount to the left, the trace line 2 for the stand indicates a leftward deflection at 28 at the time of the tail-out. The operator, in viewing the trace line, knows the nose entered stand 2 with a slight rightward movement as indicated by trace deflection 2A but entered stand 3 in a manner to cause a leftward deflection at 3A. Thus, trace line 2 at tail-out combined with trace line 3 at nose-in informs the operator of a problem in stand 2, and the problem is one of level since the lateral movement of the tail is in the same direction as the nose movement entering stand 3.

If, however, the problem in stand 2 is one of friction, the tail-out of strip 12 from stand 2 will rotate in a direction opposite to that of the nose portion 12A entering stand 3. This situation would be shown by a lateral deflection of trace 2' to the right as indicated by dash line 2C. The operator, in viewing the left swing of trace 3A evidencing the direction of the nose into stand 3 and the right swing 2C of tail from stand 2 is informed of an error in friction in stand 2. He can then intelligently and quickly, if need be, correct for such an error by adjusting the position of the scratch brushes 38 and/or 39.

The chart 33 is further effective in determining the condition of a strip entering the first stand from a prior process such as a reversing mill by a similar procedure but requires an additional comparative step. A strip having either a nonuniform cross section or a hook can cause an unbalance of a stand or stands as the nose thereof enters the stand, and also at tail-out, that would be indicated by the trace lines for the stands. Such deviations would call for adjustments outside normal operating limits of the mill It). When this occurs, the operator can take action to correct the errors in the reversing mill causing the nonuniformity of the strip.

Preferably, all the stands of the mill It) are provided with force-differential information for the tracking con trol method of the present invention. It is possible, however, to monitor the force-differentials for less than the total number of stands and yet provide good tracking control. This can be accomplished by monitoring only the upstream stands since it is in the upstream stands that the majority of strip thickness reduction takes place.

From the foregoing description it should now be apparent that a new and useful method for controlling tracking of a strip of material through a multistand rolling mill has been disclosed, the method permitting timely control before error conditions are accumulated in the mill thereby substantially reducing material waste and the possibility of costly shut down of the mill. This is accomplished by providing information of the difference of rolling force adjacent the ends of the working rolls for at least a number of the mill stands, and using this information to locate the stand and cause of the tracking problem. In this manner, correction is particularized, and the correction procedure is systematic so that additional error is not introduced in the mill by virtue of correction being performed on the wrong stand or stands. Further, by observing the rate at which the strip moves off-center, correction is limited to those occasions when the magnitude of strip movement is greater than a predetermined standard of operation for the stand or stands in question. In this manner, over correction is prevented by simply not correcting the stand or stands in question.

Though the invention has been described with a degree of particularity, changes may be made therein without departing from the spirit and scope thereof. For example, it is not necessary to provide a visual record of stand behavior. The logic of the force-differential information provided by the load cells 26, 27 and the measuring circuits 30 could be tracked by a computer. The computer could either store the information during the pass of a first strip, and thereafter perform all logic functions to effect correction of the error or error in the stands before the next strip is sent through the mill, or the computer could act immediately to correct the error while the strip being tracked is moving through the mill.

Having thus described my invention and certain embodiments thereof, I claim:

1. A method of controlling tracking of a traveling strip of material being reduced in thickness by the working rolls of successive stands of a multistand rolling mill, said method comprising the steps of measuring the roll separating force adjacent the ends of the working rolls of at least a number of said stands, and with respect to a time reference, monitoring the difference between said forces to provide time based force-differential information for each stand,

comparing the time based, force-differential information with a predetermined standard of operation for said number of stands to determine the existence and the stand location of departures from said predetermined standard of suflicient magnitude to indicate undesired stand level or frictional force conditions,

adjusting the level of a given stand when a comparison of the force-differential information of the given stand and a successive stand indicate that the nose portion of the strip entering said successive stand has tracked improperly because of a departure in the level of said given stand,

subsequently adjusting the level of said given stand by 10 an amount in the same direction as the previous adare corrected by controlling the force at which scratch justment when the force-difierential of said given brushes engage the rolls. stand indicates that the tail portion of the strip eXit- 3. The method of claim 1 in which the level of the ing therefrom has moved in the same direction as given stand is corrected by controlling the adjustment of noted for the nose portion entering said successive 5 front and back screws of the stand. stand, but when the time based force-differential information of References Cited a given stand indicates that the tail portion of the UNITED STATES PATENTS strip exiting from said stand has moved in a lateral direction While that of the nose portion entering a 10 giggg i et 72 27 X successive stand shows substantially no lateral move- 1 1? ment, or movement in the opposite direction, adjusting the distribution of frictional forces between the MILTON S- MEHR Primary Examiner strip and the Working rolls of said given stand. 2. The method of calim 1 in which the distribution of 15 US. Cl. X.R. frictional forces on the working rolls of the given stand 7227, 14 

